There are many types of electronic devices (medical devices, sensing devices, and the like) that can fail due to moisture or other environmental contaminants coming into contact with the device electronics. A common mechanism is the addition of water to contaminants that combine to form ionic solutions that are conductive and may lead to failure of the electronic device. The failure of such devices may have, in some cases, serious consequences for users of systems which contain the devices. For example, if the device is used in a medical system such as an infusion pump for the delivery of medications/drugs, a failure of the device may lead to accidental over-delivery of the medications/drugs, possibly resulting in injury or death.
One common manner of protecting electrical and electronic components and circuits in such systems against contact with moisture or other environmental contaminants involves covering the electronics of such systems with potting materials that are resistant to contaminants such as moisture. One drawback of this method is that known potting materials can fail to protect the electrical system against long-term contaminant penetration. For example, over time, moisture may diffuse through the potting material, where the penetrated moisture will likely detrimentally affect the performance of the electrical system and may lead to unpredictable and possibly dangerous system failures. Also, the potting materials may degrade, separate or pull away from and expose the electrical and electronic components and circuits, which may reduce the effectiveness of the protection by exposing the various components and system to contaminants.
The contaminant may pass by or diffuse through the potting material that covers particular electrical or electronic components which may be “critical” because they affect a critical operation of a system (i.e., the failure of which may have serious consequences). Such critical operations may include, for example, electronics for controlling a motor that, for example drives an infusion pump for delivering a medication to a patient. A resulting failure of critical electrical or electronic components due to contact with a contaminant may have serious consequences such as those described above.
As discussed above, conventional drug delivery systems such as infusion pumps are examples of systems wherein a failure of the systems' electronics may have serious consequences. An infusion pump system can include electronic control circuits and electronic power driver circuits, as well as other circuitry. The control electronics can control the power driver circuit to drive a motor which, in turn, drives the infusion pump. One such drug delivery system is used to deliver insulin over a period of time and utilizes a variety of motor technologies to drive an infusion pump. Typical motor technologies include direct current (DC) motors, stepper motors, or solenoid motors. Each motor type has various advantages and disadvantages related to cost, reliability, performance, weight, and safety.
In drug delivery using infusion pumps, the accuracy of medication delivery can be critical (such as for insulin, HIV drugs or the like), since minor differences in medication quantity can dramatically affect the health of the patient. Thus, safeguards must be designed into the delivery system to protect the patient from over or under delivery of medication. For example, in the case where insulin is administered via an infusion pump to a diabetic patient, excessive drug delivery could cause complications due to hypoglycemia, and could possibly even result in death. Therefore, controlled delivery with safeguards against over-delivery of medications is required for drug delivery systems when over-delivery could result in complications, permanent damage, or death of the patient.
In conventional systems, these safeguards against over-delivery have been incorporated into the drive systems of infusion pumps in varying ways. For example, the motor control electronics utilize cross checks, encoder counts, motor current consumption, occlusion detection, or the like, as a form of feedback to guard against over or under delivery of medication. However, one drawback to this approach can occur if the control electronics in a DC motor driven infusion pump were to fail, such that a direct short occurs from the power source to a DC motor in the infusion pump. For example, in one failure mode, it would be possible for the DC motor to drive continuously for an excessive period of time, for example, until the power source was depleted or removed, or until the short was removed. This condition is commonly referred to as motor “run away”, and could result in all of the medication contained in the infusion pump being infused immediately over too short a period of time resulting in injury or death to the patient.
To avoid this drawback, some infusion pump manufactures have avoided the use of DC motors and have instead utilized solenoid or stepper motor technologies. With these motor types, any short in the control electronics, would only result in, at most, a single motor step. Therefore, motor “run away” would not occur. Thus, this minimizes the risk of a “run away” failure. However, a drawback to the use of solenoid or stepper motor technologies is they generally have a less efficient performance with regard to battery energy, tend to cost more as compared to the DC motors, and may only be capable of running in one direction (i.e. not reversible).